Differential pressure gauges are typically known in the art for aiding in monitoring the volumes of gases or liquids. A differential pressure gauge often functions by monitoring pressure on opposite sides of a piston-magnet or diaphragm-magnet sensor. Changes in the pressure difference will normally cause the sensor assembly to move in proportion to the change.
A rotary magnet, usually located in a separate body cavity and isolated from acting pressures, is typically rotated by magnetic coupling to linear movement of the sensor magnet. A pointer attached to the rotary magnet may indicate differential pressure on an easy to read dial.
However, there is usually a lag in position and/or time between the movement of the sensor magnet and the rotary magnet because the rotary magnet follows the action of and reacts to the sensor magnet's movements. Because of this lag, the gauge is typically calibrated for measuring a pressure differential so that the lag is taken into account. If the lag is not accounted, the measurement may not be accurate.
In some instances, calibration is performed while pressure is increasing, or in the ascending direction. In other instances, calibration is performed as pressure is decreasing, or in the descending direction. Several factors may determine the direction of the pressure during calibration, such as the type of gauge, the fluid being measured, the apparatus that contains the fluid, and the like.
Because of this, operators in the field that are measuring pressure at a customer's location normally need to have at least two gauges in order to measure pressure differential since calibration may be in either the ascending or descending direction. This problem can be exacerbated if calibration needs to be performed multiple times, which may occur if the gauge is dropped or if the gauge is undergoing maintenance such as changing magnets. In some cases, the operators calibrate the gauge often because it enhances accuracy of the measurements.
What is desired, therefore, is gauge that reduces the time needed to measure pressure at the customer's location. A further desire is a gauge that reduces calibration time without sacrificing accuracy. Another desire is a gauge that is easy to calibrate regardless of the direction of the pressure. Yet another desire is a gauge that eliminates the inaccuracy caused by positional lag, where positional lag is present due to a magnet pulling in each direction and the sensor magnet must be displaced in each direction to create pull on the rotary magnet.